1. Field of the Invention
The invention pertains to the field of variable cam timing systems. More particularly, the invention pertains to a variable cam timing system where a centrifugally operated valve controls the oil flow to a locking pin.
2. Description of Related Art
Internal combustion engines have employed various mechanisms to vary the angle between the camshaft and the crankshaft for improved engine performance or reduced emissions. The majority of these variable camshaft timing (VCT) mechanisms use one or more “vane phasers” on the engine camshaft (or camshafts, in a multiple-camshaft engine). In most cases, the phasers have a housing with one or more vanes, mounted to the end of the camshaft, surrounded by a housing with the vane chambers into which the vanes fit. It is possible to have the vanes mounted to the housing, and the chambers in the housing, as well. The housing's outer circumference forms the sprocket, pulley, or gear accepting drive force through a chain, belt, or gears, usually from the camshaft, or possibly from another camshaft in a multiple-cam engine.
In some engines, the locking pins don't remain seated in the locked position, preventing movement of the rotor relative to the housing, until the engine speed is great enough. Other times, the locking pin does not lock at the appropriate time during engine shutdown, allowing the vane to oscillate within the chambers of the phaser and cause damage.
Some phasers use locking pins that utilize the aid of centrifugal force to lock the housing relative to the rotor, as shown in JP2001227311A, “Lock Pin With Centrifugally Operated Release Valve.” JP2001227311A shows a locking pin and the centrifugal force that acts on the pin during idle to aid in locking the pin quickly. The locking pin in this reference is controlled by a hydraulic force that acts on the locking pin with the aid of any centrifugal force present.